Corneal Epithelium-derived Neurotrophic Factors Promote Nerve Regeneration

Purpose To explore the corneal epithelial cells derived neurotrophic factors expression and evaluate their effects on the trigeminal ganglion(TG)neurite outgrowth and corneal nerve regeneration in normal and STZ induced diabetic mice.Methods Corneal epithelial wound healing model was build by using C57/B6 L mice.The expression of neurotrophic factors were compared among the intact,regenerating(2 days post wound)and regenerated(7 days post wound)mouse corneal epithelium.Mouse primary TG neurons were isolated and treated with the conditioned medium of mouse corneal epithelial cells.The secreted levels of nerve growth factor(NGF)and glial-derived neurotrophic factor(GDNF)were compared between the normal and wounded corneal epithelial cells.NGF neutralized antibody and GDNF blocking peptide was used to evaluate their roles in mouse corneal nerve regeneration and TG neurite outgrowth.Diabetic mice were induced by STZ.The NGF and GDNF expression were compared between normal and diabetic corneal epithelium.The promoting effects of NGF and GDNF for the corneal nerve regeneration were further evaluated in the diabetic mice.Results The expression of NGF and GDNF showed the most significant up-regulation in the regenerating corneal epithelium(2 days post wound)and return in the regenerated epithelium(7 days post wound).In addition,blocking either NGF or GDNF significantly suppressed corneal nerve regerneration and epithelial wound healing.The conditioned medium of corneal epithelial cells promoted the TG neurite outgrowth with extended branching and elongation.However,the blockage of either NGF or GDNF significantly impaired the promotion of the neurite outgrowth by the conditioned medium.Moreover,both NGF and GDNF expression were attenuated in the diabetic regenerating corneal epithelium,while exogenous NGF or GDNF administration promoted the corneal epithelial and nerve regeneration in diabetic mice.Conclusion Corneal epithelium expression and neurotrophic factors it releases can facilitate corneal nerve regeneration,and NGF and GDNF play important roles in it..